1. Field of the Invention
The present invention relates to a rotation angle detecting device that is used for detection of a rotation angle of a rotary body provided in a vehicular apparatus, such as detection of a steering angle of a vehicle steering wheel.
2. Description of the Related Art
A rotation angle detecting device is known that is used for detection of a rotation angle of a rotary body provided in a vehicular apparatus, such as detection of a steering angle of a vehicle steering wheel. This rotation angle detecting device is provided with a disk-shaped code plate that rotates together with the rotary body and is formed with a slit array as a track for generating a signal and a detecting means for detecting a rotation angle of the rotary body based on a signal that is generated by rotation of the code plate.
In the above conventional rotation angle detecting device, the slit array is formed in the disk-shaped code plate in such a manner that slits are arranged in the circumferential direction of the code plate. The detecting means is provided with a light-emitting element that is disposed at a prescribed position and emits light toward a slit and a light-receiving element for receiving light that has been emitted by the light-emitting element and has passed through a slit.
To increase the resolution, the code plate is provided with a plurality of slit arrays such as a slit array as a incremental signal track and a slit array as an index signal track.
Incidentally, to install the conventional rotation angle detecting device in an automobile or the like, it is necessary to set the dimensions of the entire device in accordance with limitations on the installation space that are caused by layout relationships with peripheral devices and other factors. Further, to control an associated vehicular apparatus with high accuracy in accordance with the rotation angle of the rotary body, the accuracy of detection of the rotation angle of the rotary body needs to be high.
However, to give high detection accuracy to the rotation angle detecting device, the accuracy of working that relates to the shape and arrangement of slits that are provided in the disk-shaped code plate and the accuracy of working that relates to preventing the code plate from becoming eccentric should be high to a certain extent; the code plate becomes more difficult to work as its diameter becomes smaller. In particular, where the code plate is provided with a plurality of slit arrays, the diameter of the code plate tends to be large. That is, it is difficult to reduce the dimension of the rotation angle detecting device in the radial direction of the code plate.
The present invention has been made to solve the above problems, and an object of the invention is therefore to provide a rotation angle detecting device capable of increasing the resolution without increasing the diameter of a code plate.
To attain the above object, the invention provides a rotation angle detecting device comprising a cylindrical code plate that rotates as a rotary body rotates, the code plate having a circumferential side portion that is provided with a plurality of slit arrays that are arranged along a rotation axis of the code plate, each of the slit arrays having slits that are arranged in a circumferential direction of the code plate; a light-emitting portion provided at a prescribed position for each of the slit arrays, for emitting light toward a slit of the slit array; and a light-receiving portion provided for each of the slit arrays, for receiving the light that has been emitted by the light-emitting portion and has passed through the slit.
With this configuration, the dimension of the portion where the plurality of slit arrays such as a slit array as an incremental signal track and a slit array as an index signal track are formed can be included in the dimension of the code plate along its rotation axis rather than the diameter of the code plate. Therefore, high resolution can be attained without increasing the diameter of the code plate.
The above rotation angle detecting device may be such that the plurality of slit arrays are two slit arrays, and that the slits of one of the two slit arrays are cuts that are formed at one end of the circumferential side portion so as to extend along the rotation axis of the code plate, and the slits of the other slit array are cuts that are formed at the other end of the circumferential side portion so as to extend along the rotation axis of the code plate.
With this configuration, when a code plate is formed by resin molding using a molding die, a cylindrical code plate having two kinds of slit arrays can be formed without the need for using a slide core for forming slits. The structure of the molding die is simple and the number of manufacturing steps is smaller. As a result, the manufacturing cost of the rotation angle detecting device can be reduced.
In the above rotation angle detecting device, it is preferable that one of the two slit arrays be an incremental signal track and the other slit array be an index signal track. This configuration makes it possible to detect an absolute rotation angle at a high resolution using plural numbers of rotations.
The above rotation angle detecting device may be such that the cylindrical code plate further has a top planar portion, and that the cuts of the incremental signal track bridge the top planar portion and the circumferential side portion and the cuts of the index signal track are adjacent to an opening of the circumferential side portion.
With this configuration, each slit of the incremental signal track is completely closed. The code plate can be made stronger and hence its deformation due to external force or the like can be reduced. And it becomes possible to detect an absolute angle at a high resolution with high accuracy.
The first-described rotation angle detecting device may be such that at least one of the light-emitting portions be disposed inside the cylindrical code plate and at least one of the light-receiving portions be disposed outside the cylindrical code plate, and that the at least one light-receiving portion receive light that is emitted by the at least one light-emitting portion and travels somewhat upward with respect to a horizontal direction in a state that a top planar portion of the cylindrical code plate is oriented horizontally.
With this configuration, since the light-emitting portion is set lower than the light-receiving portion, the dimension of the cylindrical code plate along its rotation axis can be reduced. Therefore, the dimension of the rotation angle detecting device along the rotation axis of the code plate can be reduced.
In the above rotation angle detecting device, it is preferable that one of the two slit arrays be an incremental signal track and the other slit array be an index signal track. In addition to the above-described advantages, this configuration provides an advantage that an absolute rotation angle can be detected at a high resolution by using plural numbers of rotations.
In the above rotation angle detecting device, it is preferable that the cylindrical code plate further have a top planar portion, and that cuts as the slits of the incremental signal track bridge the top planar portion and the circumferential side portion and cuts as the slits of the index signal track be adjacent to an opening of the circumferential side portion.
With this configuration, each slit of the incremental signal track is completely closed. The code plate can be made stronger and hence its deformation due to external force or the like can be reduced. Another advantage is that an absolute angle can be detected at a high resolution with high accuracy.